Effects of groundwater flow on thermal response test of deep borehole heat exchanger

Abstract

Deep borehole heat exchanger (DBHE) has a great potential to exploit geothermal energy, and although many studies are conducted on DBHE, the effects of groundwater flow on thermal response test (TRT) results of DBHE remain to be uncovered. This paper utilizes a numerical model to simulate TRT of a DBHE with groundwater flow, and the simulated TRT data are used for estimation of effective ground thermal properties based on a parameter estimation method and a semi-analytical heat transfer model, and then the effects of groundwater flow on the TRT results of DBHE are investigated under different conditions. When Darcy velocity is high enough, groundwater flow would lead to overestimation of effective ground thermal conductivity and underestimation of effective volumetric heat capacity of ground, and the effective ground thermal properties have larger error for higher Darcy velocity and longer test duration, and using the effective ground thermal properties would underestimate the long-term DBHE performance. The effect of groundwater flow on the TRT results of DBHE is greater for lower ground thermal conductivity and lower volumetric heat capacity of ground, and is slightly influenced by other parameters. The results of this paper offer some guidelines for TRT of DBHE with groundwater flow.